W1209 style NTC sensor signal to temperature conversion with LPF and un-chatter (GND -- NTC -(Ain)- 20k -- VCC)

ntctheta

\ W1209 temperature measurement with filter and noise suppression
\ © 2017 TG9541, refer to https://github.com/TG9541/W1209/blob/master/LICENSE

\ Note: W1209 thermostats may require adjustment,
\       especially when used outside the range of -5C to +20C
\       Refer to https://github.com/TG9541/W1209/wiki/W1209-Sensor

RAM

  900 CONSTANT USENSMAX \ max temperature

NVM

#require @inter

  $8000 CONSTANT DEFAULT   \ Default value indicator (-32768)

  \ note: adjust to specific sensor here if accuracy is required!
  \ note: @inter accepts 2..n value pairs
  \ interpolation table ADC digits * 32 -> temperature * 10
  CREATE dig2tem  14 ,  \ number of value pairs
          1216 , 1100 ,  \  1  1216 -> 11.0 C
          1534 , 1000 ,  \  2
          1982 ,  900 ,  \  3
          2560 ,  800 ,  \  4
          3296 ,  700 ,  \  5
          4320 ,  600 ,  \  6
          5634 ,  500 ,  \  7
          7370 ,  400 ,  \  8
          9632 ,  300 ,  \  9
         12382 ,  200 ,  \ 10
         15522 ,  100 ,  \ 11
         19012 ,    0 ,  \ 12
         20768 ,  -50 ,  \ 13
         22466 , -100 ,  \ 14  22466 digits -> -10.0 C

  : lpf32 ( n1 alpf -- n2 )
    \ low pass filter, multiplies n1 by 32, uses a as LPF memory
    ( alpf ) DUP >R @ DUP 32 / - + DUP R> !
  ;

  : unchatter ( n1 ahy -- n2 )
    \ remove chatter (+/- 0.5 digit window), divides n1 by 32
    \ ahy: hysteresis storage call address 
    SWAP 16 / OVER @ OVER SWAP - ABS  2-
    0< IF DROP @ ELSE DUP ROT ! THEN
    2/
  ;

  : ntctheta   ( adc astr -- theta )
    \ filter noisy W1209 sensor input, result in astr @  

    SWAP DUP USENSMAX < IF
      OVER 2+        lpf32     \ low pass filter, "noise to digits", 32*ADC
      dig2tem @inter           \ interpolation: lpf32 digits to temperature
      OVER 2+ 2+     lpf32     \ low pass filter, "smoothen", 32*theta
      OVER 2+ 2+ 2+  unchatter \ remove chatter, divides by 32
    ELSE
      DROP DEFAULT      \ sensor error - default
    THEN

    SWAP !                \ store theta in astr
  ;

RAM